The hand alone is faster to move, but if you drag your whole body with it in unison it simply slows you down...
Throw the reaction time into the plate simply put can you reach the opponent's pressure points with sufficient manipulation or impact force before they manage to evade or deflect it? Well immediately you should think now that deflection involves mostly one limb vs. the whole body which is easier to drag faster to create a sort of a barrier to attacks...
My first Martial Arts Instructors were smooth, impressive, had black belts, were champions in sports and fighting sports, and perhaps or most likely as a Jew among non Jews or even Jew among Jews had street bullying taste and street fights.
But the separation of the two and the continuing to follow the traditional fighting sports or exhibition martial arts send me to a 7 years trip to the moon. It was a total distraction!
What is bullying? Cheap talk, intimidation with intent to punch your or throw you to the floor and humiliate you in person or in public and sometimes more severe than that.
What would be the appropriate training then? Obviously you can just let yourself be bullied until you are willing no more! And then you try and do something. If it does not succeed, you go to the hospital or morgue and try again until you learn on your own.
What is wrong with this approach? Its too risky! You can have an irreparable damage. You can keep getting bad habits by not trying in a good enough way from the first try and its also hard to keep track to figure out if you succeeded because your opponent was less efficient than you or you were the most efficient in your action.
You can take martial arts or fighting sports - but that might help your motivation for fitness breaking boards or hitting someone with gloves or trying to armbar an opponent until he gives up.
There are a lot of other elements thrown into the plate when you encounter a threat. You are alone for few split seconds. These split seconds could determine your life or death experience. These split seconds could end quickly in a win or a loss, or could last longer in humiliating matter and then end with emotional loss of dignity, sense of worthiness which will harm greatly your future efforts in life, and physical disability and death.
In this environment neither you and neither your opponent are supervised by anyone! It is all up to you then since you dont know what your opponent is capable of committing!
So how about have an acting class where you get verbally abused, learn to talk dirty back and have a contest of slaps and slurs until you gain your confidence back?
Well cheap talk is cheap. But you need to learn how to stop it if the volume gets too high. You also need to learn how not to get physically hurt when things turn physical.
So really it is not about having more sparring for a trophy or for the exercise ,nor pumping iron for instilling fear of your physique. But rather breaking down what every human does in a confrontation and use the meaningful breakdown to the advantage of your training.
Its not being able to keep a poker and tough face against variety of intimidating faces and bodies. Instead you need the kind of training that teach you to look at the physical and invisible processes that happen in a confrontation and gear your training specifically for that. This is exactly what you do in Pure Krav Maga.